1. Field of the Invention
The present invention is generally related to a front-end circuit for a transceiver, and more specifically to a low-power transceiver front-end that can be implemented on a single substrate without the need for buffer amplifiers.
2. Background Art
Electronic communication systems include transmitter and receiver circuits. In many communication systems, transmitters and receivers are present in every node of the system and are often combined to form what is called a transceiver.
A transceiver front-end is a circuit that interfaces a transmission medium with both the receiver and transmitter of a transceiver. Exemplary transmission mediums include a cable, optical fiber, antenna, etc.
There are typically two input signals to the transceiver front-end, a receive signal and a transmit signal. The receive input signal comes from the transmission medium and is intended for the receiver portion of the transceiver. The transmit input signal comes from the transmitter and is intended to exit the transceiver to a transmission medium. Therefore, the transceiver front-end is necessarily a three-port device, where a first port connects to the transmission medium, a second port connects to the receiver, and a third port connects to the transmitter. It is important that the receiver port is sufficiently isolated from the transmitter port, so that the transmit signal is not an input to the receiver.
A conventional transceiver front-end has some known limitations. For example, the typical front-end will have one or more buffer amplifiers to provide amplification and/or isolation between front-end components. Each buffer amplifier consumes power and generates unwanted heat that should be removed from the substrate. Furthermore, it is often desirable to integrate multiple transceivers onto a single substrate to increase integration. When multiple transceivers are integrated on a single substrate, it is critical to make each transceiver as low-power as possible to prevent the need for a blower or heat sink on the chip.
Furthermore, buffer amplifiers are active devices that generate added noise that can degrade overall system noise figure. At the front-end, the added noise is especially detrimental to the overall system noise figure.
Still further, it is necessary that the buffer amplifiers have sufficient dynamic range to cope with input signals having widely varying amplitudes so as to prevent signal distortion. The dynamic range requirement can complicate the buffer amplifier design and the design of the transceiver front-end. More specifically, more power is required to limit signal distortion.
In summary, the elimination of buffer amplifiers will not only save power, heat sinks, blowers, and chip area, but will also relax the noise and distortion requirements of the other circuits in the chain. A preferred transceiver front-end would use as few buffer amplifiers as possible for these mentioned reasons.
What is needed is a scalable transceiver front-end that permits the reduction or elimination of buffer amplifiers, resulting in signal processing that uses close to zero power and has very low distortion and noise.